Photomechanical resist



Patented July 10, 1934 UNITED STATES PHOTOMECHANICAL RESIST Alexander Murray, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New York .No Drawing. Application January 21, 1931,

Serial No. 510,336

Claims.

This invention relates to a photo-mechanical resist or light sensitive enamel, such as is'used in coating metal, light printing upon it from a halftone or line negative, developing, and then 5 etching.

' An object of the invention is the provision of a light'sensitive enamel to replace the well known bichromated type of resist which has hitherto been used. As an example of the latter, fish glue and ammonium bichromate have been employed.

Other colloids have also been used with bichromates. Another type of resist has consisted of certain light sensitive resins with sensitizers. Still another type is exemplified by Syrian asphaltum. In general, previous work in this field has depended upon the use of photo-sensitive organic materials in the colloidal or resinous state. As is well known it is difiicult to prepare compounds in this state of absolutely uniform composition and characteristics. Commonly, the

composition is not even definitely known.

In the present invention, I use compounds of relatively high. purity, whichgmay generally be obtained irithe crystalline state, and combine with thenY'a substance or substances which inhibit or prevent the crystallization, make it possible to obtain a coating of a continuous film, and which cause the light sensitive compound to have a higher sensitivity than it would have in the crystalline state. The light sensitive compounds which are used are more or less well known for their property of light sensitivity, and many of p the inhibitors which I add have been previously used in photo-mechanical resists.

The combination of these two types of substances is; however, new, and I produce from this combination a new result in that I prevent. the light sensitive material from crystallizing and thereby obtain a continuous film of enhanced sensitivity having marked advantages.

The light sensitive substances which I use are complex unsaturated organic compounds of definitely known composition, in many cases it having been previously known that these materials are sensitive to light. These substances contain an ethylene linkage Most of these substances show the property which is known as stereoisomerism, and under the action of light are converted from one isomer into another. As stated above, these properties have been previously described. For example, in 1895 C. Liebermann was so impressed by thesensitivity of certain photo-polymerizations, notablythe conversion of allo-cinnamylidine-acetic acid H CH 0 H H0.0C- -H into trans-cinnamylidineacetic acid in benzol solution that he forecast a photographic use for the reaction. (Berichte'28, 1447.) In spite of this early prediction, however, very little practical use has been made of compounds of this type largely because of the very slight sensitivity of the materials when in crystalline state and their tendency to crystallize.

Compounds of the above-described class which give excellent results are the following: Anisal cinnamyl acetone, piperonylidine aceto-phenone, Cinnamylidine aceto-phenone, Benzylidine acetophenone, Iso (cis) cinnamal acetic acid.

These compounds are not directly applicable 0 to the purpose of forming a continuous sensitive film. They crystallize when the volatile solvent evaporates-and in the crystalline state are only slowly affected by light.

I have found that if the substances can be maintained in a non-crystalline condition during exposure, they are much more sensitive to light. This and the means of doing it constitute. in part the present invention.

A powerful inhibitor of crystallization is isonitroso acetophenone. One part of this to eight parts of anisal cinnainyl acetone, for example, is sufficient to prevent crystallization when the solvent evaporates. The film thus produced has some of the properties of a supersaturated solution. Copal resins are also inhibitors of crystallization, as are a number of other resins and gums. Some examples of gums and resins which I may employ are Cumar resin, ntiniak copal resin, and Kauri gum.

I do not limit myself by the examples given, as it is understood that other light sensitive substances and other gums and resins are useful.

While certain phases of the reaction which my sensitive layer undergoes are not perfectly understood kbelieve that the first action of light on the light sensitive substance is to convert it from one isomer into another, and that on further exposure the second isomer is caused to polymerize. One possibility, in which two of these isomers are polymerized to a dimer is shown by the following reaction:

tics of the film. It is believed that the noncrystalline film may be regarded as a solid solution, a fluid or plastic eutectic or a supercooled liquid. Whatever view may be taken as to the state of this film, it is only important, and a part of this. invention, that the sensitive compounds are maintained in the non-crystalline state duringexposure.

A general formula for practical use as a cold enamel in photo-mechanical work is:

Crystalline p h t o sensitive .compound 1.0 grams Non-sensitive inhibitor of crystallization. 0.5 to 10.0 grams Acetone c.c.

Most of the substances mentioned will give satisfactory results if used in accordance with this general formula.

Other specific formulas which give excellent results are the following:

. Example} Anisal cinnamyl acetone 2.0 grams Piperonylidine acetophenone 4.5 grams Kauri copal XXX 3.0 grams Cumar resin, varnish grade, hard 0.3 grams Ethl methyl ketone 25 c. c. Benzol 25 c. c.

Acetone 50.0

Another formula is:

Example If Piperonylidine acetophenone 1.0 grams Pontiniak copal 0.5 grams Ethyl methyl ketone 5 c. c. Acetone 10 c. c. Benzol 5 c. 0.

Another formula is:

Example III Michlers ketone' 1.0 grams Cinnamaldehyde 0.5 grams Pontiniak copal 0.5 grams Benzol 10 c. c. ,Aimhnl 5 c. c.

"tetra methyl diamino benzophenone A formula which is cheaper is the following:

. between 15 seconds and 1 minute.

In this formula the coumarin or m-nitro-benzaldehyde are used as a diluent and to make development easier.

Various substances may be used with the materials mentioned, as diluents or modifiers. may be employed either to reduce the costof the enamel, or to modify its characteristics. Such substances are for example, coumarin, m-nitrobenzaldehyde, p-nitroaniline, p-naphthol, p-nitro acetanilide, nitro-brom-benzene and p-nitro phenol.

A method of using these enamels is as follows: The metal, copper or zinc is scrubbed with pumice and water, rinsed, and the water polished off with a towel. Drying the water off on a whirler appears less satisfactory. After the metal plate is dry it is coated with one of the enamels given above, in an amber or-orangelight. The plate is then dried without heat in the dark for at least five minutes.

The plate is next exposed to an image, as under a suitable negative or by projection, to a strong light source, such as an arc, the exposure varying with the particular enamel used and usually lying To develop, mineral oil is spread all over the print. This is kept in motion over the surface with absorbent cotton, being careful not to rub with too much force. Within one-half minute the unexposed part will become opaque and clearly visible. Development is continued for three minutes. Considerable pressure is now applied to the swab and the opaque areas come away. When all the opaque spots have been removed, the plate is then washed with soap and water and wiped dry. The

plate is now ready to etch and the known. image areas will begin to etch instantly all over, when exposed to the etching fluid.

Advantages to be secured bythe use of enamel made in accordance with this invention are as 5 follows:

1. The enamel will stand any amount of treatment with nitric acid under 50% strength, and any amount of etching in ferric chloride.

2. It will stand the scrubbing of re-etching o brushes.

3. It will stand most water solutions, but not solvents, except paraifine and petroleum oils.

4'. Because it is not brittle it does not chew" at the edges in zinc etching, but etches with a sharp even edge, giving perfectly formed dotsin single-bite etchings.

5. It has a faint, pleasant aromatic odor, whereas many of the resists in use heretofore have a particularly strong and offensive odor.

In addition to these advantages, the sensitivity can be varied by adding more or less of the inactive substances or solvents. It is thus possible to obtain an enamel which prints within any time over a wide range.

Among substances which may be mentioned as modifiers are cellulose derivatives. Tackiness and solubility in the developer can be reduced by adding small proportions of cellulose ester solutions. As an example, 2 grams of 8% cellulose nitrate in acetone are added to Example IV.

I consider as included within my invention all variations and equivalents coming within th scope of the' appended claims.

What I claimis:

1. A photo-mechanical resist comprising, in a layer which is to be exposed to a light image, a crystallizable halogen-free organic light-sensitive substance capable of autogenic formation of insoluble chemically resistant non-crystalline prod- These 80 ucts of higher melting point. when exposed to light, together with a chemically indifferent substance which inhibits the crystallization of the light-sensitive material, so that said light-sensitive material is maintainedin a non-crystallized state during exposure.

2. A light sensitive composition including in a non-crystalline state an unsaturated organic compound, light sensitive in itself, having the tendency'to crystallize, and having the property when in non-crystalline state of isomerization under the influence of light and having such property to a very much less extent when in the crystalline state and a colloidal substance which inhibits the crystallization of the compound.

3. A composition for use as a photo-mechanical, light sensitive resist, including in solution an organic compound containing the ethylenelinkage saidsubstance' being light sensitive in itself, and.

having the property when in non-crystalline state of isomerization under the influence of light, and having such property to a very much less extent when in the crystalline state, and having a tendency to crystallize out of the solution, and a colloidal substance which inhibits the crystallization of the compound. I

4. A light sensitive composition for use as a photo mechanical resist and including in solution a ketone containing the linkage the ketone when in non-crystalline 'state being in itself light sensitive and when in crystalline state being light sensitive to a very much less extent, and a colloidal substance which inhibits crystallization of the ketoner 5. A light sensitive composition including in solution a ketone containing the linkage the ketone when non-crystalline state being in itself light sensitive and when in crystalline state being light sensitive to a very-much less extent and a'resin which inhibits the crystallization of the ketone.

6. A light sensitive composition includingin solution an organic substance, capable when in noncrystalline state, when exposed to light, of autogenic formation of insoluble chemically resistant non-crystalline products of higher melting point,

said substance having a tendency to crystallize and being substantially not light sensitive when in a crystalline condition, together with a colloid material which is inert with respect to the chemical or light sensitive properties of said substance, but which inhibits its crystallization.

7. A sensitive element comprising a support and a solid sensitive layer thereon, said layer comprising in a non-crystalline state an unsaturated organic. compound, light: sensitive in itself, having a tendency to crystallize, having when in non-crystalline state, the property of isomerization under the influence of'light and having such property to a very much less extent when in crystalline condition and a colloid carrier which inhibits the crystallization of the compound.

8. A sensitive element comprising a support and a solid sensitive layer thereon, said layer including in a non-crystalline state an organic substance capable, only when in such state, of energetic autogenic formation of insoluble chemically resistant non-crystalline products of higher melting point, said substance having a tendency to crystallize, together with a colloid material which is inert with respect to the chemical andlight sensitive properties of said substance but which inhibits its crystallization.

9. A sensitive element comprising a support and a solid sensitive layer thereon. said layer comprising in a non-crystalline state -a ketone containing the linkage \C=IC. I said ketone being in itself appreciably light sensitive only when in a non-crystalline state and having a tendency to crystallize, together with a colloid material which is inert with regard to the chemical and light sensitive properties of said ketone but'which inhibits its crystallization.

- 10. A sensitive element comprising a support and asolid sensitive layer thereon, said layer comprising in a non-crystalline state a ketone containing the linkage v \C'=C/1 the ketone being in itself appreciably light sensitive only when in a non-crystalline state and having a tendency to crystallize, together with a resin whichis inert chemically and photogenically toward the ketone but inhibits its crystallization.

. ALEXANDER MURRAY. 

